A currently-existing problem consists in providing a reliable control mechanism for the compound transmission for a transport vehicle fitted with a main gearbox and a tandem-connected auxiliary two-range gearbox with high-gear and low-gear ranges.
Transmissions of this type are most characteristic of the motor trucks of medium and high load-carrying capacity. The tandem connection of the auxiliary two-range gearbox with the main gearbox doubles the total number of speeds in the transmission thus improving the running performance of the motor truck and its fuel consumption within a broad range of its service conditions.
However, the necessity of simultaneous control of two gearboxes, the main and auxiliary ones, complicates the control mechanisms of such compound transmissions, thereby impairing their reliability.
Known in the prior art is a control mechanism of the compound transmission for a transport vehicle (DE, C, 1195177) comprising a main gearbox and an auxiliary two-range gearbox connected in tandem to said main gearbox and having a high-gear range and a low-gear range.
The main gearbox providing for four forward speeds comprises constant-mesh gears mounted on parallel rotating shafts, and two gear couplings, one for alternate engagement of two forward speeds and the other one for alternate engagement of two additional forward speeds. The auxiliary two-range gearbox is a planetary mechanism and has a toothed coupling intended for alternate engagement of the low-gear (step-down) range and a high-gear (direct speed) range.
The control mechanism of this compound transmission comprises a casing, a hand lever articulated with said casing, a shaft installed in the casing, said shaft being linked kinematically with the hand lever and having pins engaging the drive links of the toothed couplings of the main gearbox, a pneumatic actuator for moving the toothed coupling of the auxiliary two-range gearbox, and a system of valves for controlling said pneumatic actuator.
The hand lever has a handle operated by the vehicle driver and is installed on the casing of the transmission control mechanism so that the lever can be shifted over a "double-H" path. On shifting the lever handle in a transverse direction, the lever turns the shaft so as to select the speeds in the main gearbox, while on longitudinal movement of the lever handle, said lever moves the same shaft axially in one direction or other so that the selected speed is mechanically engaged in the main gearbox.
On shifting the lever handle over one half of the "double-H" path, the speeds are successively engaged in the main gearbox at one range of the auxiliary two-range gearbox. When the lever handle is shifted transversely from one half of the "double-H" path to its other half, the valves control the pneumatic actuator intended to change ranges in the auxiliary two-range gearbox. As the lever handle is further moved over the second half of the "double-H" path, again the main gearbox speeds are successively engaged but now in the other range of the auxiliary two-range gearbox.
The above-described control mechanism of the compound transmission provides for simple control of a transmission with a large number of speeds by shifting the hand lever handle through the same path as that of the hand lever handle of a transmission having half as many speeds.
However, in case of failure of the pneumatic actuator or of one element of the system of valves controlling said pneumatic actuator, it becomes impossible to shift the ranges in the auxiliary two-range gearbox.
In such a case, when the high-gear range is engaged the vehicle will be unable to start from rest and move at a low speed to a repair shop.
Another known control mechanism of the compound transmission for a transport vehicle (DE, C, 3000577) has a main gearbox and a tandem-connected two-range auxiliary gearbox with the high-gear and low-gear ranges.
This mechanism comprises a casing, a first and second sliders which slide in the casing and serve for engaging four forward speeds in the main gearbox, a third slider for engaging the reverse speed in the main gearbox, also a shaft kinematically linked with the hand lever for the selective shifting of the first, second and third sliders from the neutral position to the gear-engaging positions and back, said shaft being installed in the casing with a provision for rotation and axial movement.
There is a valve for controlling the pneumatic actuator of the auxiliary two-range gearbox, said valve being installed on the casing and operated by a cam connected with the shaft.
The third slider in this mechanism can be used for engaging an auxiliary fifth forward speed in the main gearbox which, as well as the reverse speed, can be engaged only in the low-gear range of the auxiliary two-range gearbox. The auxiliary fifth forward speed in the main gearbox in combination with the low-gear range of the auxiliary gearbox provides for the lowermost, the so-called "creeping" speed in the transmission.
The provision of the third slider in the control mechanism of the compound transmission widens the service capabilities of said transmission.
However, this control mechanism also does not ensure the possibility of shifting ranges in the auxiliary two-range gearbox in case of failure of the pneumatic actuator.
Still another known control mechanism of the compound transmission for a transport vehicle (DE, C, 3333423) comprises a main gearbox and a tandem-connected auxiliary two-range gearbox with high-gear and low-gear ranges.
This control mechanism of the compound transmission comprises a casing, the slide-fitted first and second sliders for engaging the forward speeds in the main gearbox, the third slider for engaging the reverse speed in the main gearbox and the fourth slider for throwing in the low-gear range and high-gear range in the auxiliary two-range gearbox.
The known control mechanism of the compound transmission comprises a drive element kinematically connected with the hand lever and intended for selective shifting of the first, second and third sliders from the neutral position to the speed-engaging positions and back, said drive element being movably installed in the casing.
The mechanism also comprises an actuator for shifting the fourth slider to the low-gear and high-gear range engaging positions, said actuator being controlled by said drive element.
Said drive element in said known control mechanism of the compound transmission has the form of a shaft installed in the casing with a provision for rotation and axial movement. The hand lever has a handle shifted manually over the "double-H" path transversely between several neutral positions and longitudinally from each neutral position to the required positions of engaging the gearbox speeds.
The shaft and the hand lever are kinematically linked by a device providing for axial movement of the shaft during said transverse shifting of the lever handle and for turning said shaft during the longitudinal shifting of said lever handle.
The actuator for shifting the fourth slider in the known control mechanism of the compound transmission is made in the form of a double action pneumatic cylinder whose piston is linked with the slider.
This known control mechanism of the compound transmission for a transport vehicle provides for engaging up to nine forward speeds and one reverse speed by means of the manually operated hand lever which is shifted similarly to the hand lever in other known transmissions with a lesser number of speeds and by means of an actuator powered by its own source of energy and is controlled by a hand lever.
However, in case of failure of the actuator or its source of energy, it becomes impossible to shift the ranges in the auxiliary two-range gearbox. If failure has occurred in the high-gear range of the auxiliary two-range gearbox, the transport vehicle cannot start from rest and move at a low speed to a repair shop.